The former England captain was sacked by Birmingham in January.
Scrum dominance proved decisive as the Sharks became the first South African side to win a major European rugby trophy by beating Gloucester 36-22 in Friday's Challenge Cup final in London.I haven't won any trophies in South Africa so being with the Sharks first year back, it's unbelievable," added Koch, who twice lifted the elite European Champions Cup with London club Saracens.
The 19-year-old finished ahead of Lois Toulson and Eden Cheng.